It’s more complicated than that. They are multi-dimensional beings and the MUST coalesce into a form we can understand to interact with us. They are more akin to concepts than entities. It’s not that they shape shift as much as our perception of them shifts.

Imagine them like your player character in a game. You can change the way your character looks to people in game, but you still are an entity outside of the game with your own form. No matter what you do, your avatar form is limited to the dimensions and constraints of the game to the others who see you in game.

So if an angel is the angel who transports God, you could interpret it many ways. I usually see carts being pulled by wheels. Okay so my mind interprets them as wheels. Okay but they can move all directions, not just back and forth. Okay so they are wheels within wheels. Okay but they are not wheels, they are still beings that are strong and wise. Strong like an ox, majestic like a lion, sharp as an eagle, with the similarity to humans.

We literally can’t comprehend their true form and it short circuits our brains and our brains have to just fill in the gaps based on our perception of the concepts they exemplify.